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힌트: 여러 단어는 쉼표로 구분
Date
예: 06/23/2022
Date
예: 06/23/2022
Global
China (简体中文)
Japan (日本語)
Korea (한국어)
Taiwan (繁體中文)
이메일
What is Cell Balancing?
So today I want to talk about cell balancing-- what it is and why it is needed. What does cell balancing mean? The use of the term cell balancing is used in conjunction with more than one series cell or group of parallel cells. It is not usually referred to with regards to balancing parallel cells. So we would look at two series or more for this application. And to balance, what do we do? We bring certain parameters of the series cell elements into equilibrium. So what do we bring into equilibrium? As the cell balancing algorithm, we can use several criteria. First of all, the most common is series cell voltage. But there's also series cell impedance, series cell maximum chemical capacity, and also series cell state of charge. When we talk about the series cell in this case, we are talking about one series and as many or as few cells in parallel. Again, we do not distinguish parallel cells. To bring the cells into balance with the chosen criteria, equal does not necessarily mean everything is exactly the same to a finite value. What we actually look at is some allowable variance-- for example, 10 millivolts, so 10 milliohms, or for capacity, 10 milliamp powers. This we would deem equal. In medium and larger format batteries, we have modular designs where cells within one module would be balanced under the chosen criteria and then each module would be then balanced with respect to each other under those same or maybe different criteria. Why is balancing needed? So this is the key topic here. Not all cells are made equal. There's a variety of reasons, such as cell to cell variation from manufacturing, connectivity from one design to the next from top cell, middle cells, bottom cells all having different length wires, different connectors to the PCB. This still is considered cell to cell variation, which needs to be accounted for. There are system environmental conditions, such as heat distribution as can be seen from the diagram. There's also when you look at larger format batteries, there could be even wider variation of either self-heating or system level localized heating. The main reason for balancing is to protect from overvoltage and undervoltage stress. There's safety features that can prevent excessive overstress that doesn't increase the rate of degradation or even cell failure. However, generally they do not prevent a low rate of degradation, which is where the soul balancing functions come in. Enables greater energy to be used. This is a key marketing factor for all battery systems. How much energy can you get from one battery, how fast can you charge and how much energy can you charge into a battery in a single cycle is very important. So therefore, all cells reaching an overvoltage or a maximum voltage state or an undervoltage state at the same time is the ideal scenario for the longer run time or the faster, most energy received battery charging time. So for the end user, the main benefits for cell balancing is extending battery life. And that can be described in two ways. A single cycle, again where you can charge, put the most energy into the battery by keeping the cell voltages below any protection cutoff or charge maximum, charging voltage cutoff. And also on the discharge side by making sure all cells reach an undervoltage state or a low voltage cutoff to the system at the same time. In this case, the weakest cell is not winning and therefore causing cell energy to be remaining in the battery. Also, longevity. A battery that is stressed from overvoltage or undervoltage becomes weaker over time, and the usable capacity will fade more quickly. In this case, then the battery would need to be replaced and therefore maybe within warranty periods cause an additional loss to the company. A failed battery in the diagram shows how a three-year-old battery with maybe a few tens to 100 cycles with a severe cell voltage imbalance has caused a vent in one of the cells. And this can be seen as quite damaging to the cell. This in particular is a power tool battery that has caused a hazard. So reduced risk from safety hazards has been a major factor. This is primarily because of industrial standards, safety standards, and of course, the risk for personal injury. Overvoltage stress over temperature stress are the two main causes of safety hazards. And obviously, cell balancing in this case will at least reduce the overvoltage stress and keep from voltage causing an additional temperature stress. There's been several studies in the market for this sort of scenario where different imbalances can be shown in various papers to have caused various faults from a cell imbalance leading to hazards. So this is why we believe cell balancing is a very important factor within a battery management system. There's additional reference material to detail the exact algorithms and the exact criteria. And the method of the way we transfer energy between cells available on ti.com. Thank you very much.
설명
2017년 1월 13일
What is battery cell balancing? What it is and why it is needed?
추가 정보
Blog: How active and passive cell balancing works
Blog: Cell Balancing: Better safe than sorry (Part 1)
Blog: Cell Balancing: Better safe than sorry (Part 2)
Blog: Battery management for questionable batteries
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